Multilocus variable-number tandem repeat analysis of Vibrio cholerae O1 El Tor strains harbouring classical toxin B

Abstract

Atypical Vibrio cholerae O1 strains -hybrid strains (strains that cannot be classified either as El Tor or classical biotype) and altered strains (El Tor biotype strains that produce classical cholera toxin) -are currently prevalent in Asia and Africa. A total of 74 hybrid and altered strains that harboured classical cholera toxin were investigated by multilocus variable-number tandem repeat analysis (MLVA). The results showed that the hybrid/altered strains could be categorized into three groups and that they were distant from the El Tor strain responsible for the seventh cholera pandemic. Hybrid/altered strains with a tandem repeat of the classical CTX prophage on the small chromosome were divided into two MLVA groups (group I: Mozambique/Bangladesh group; group III: Vietnam group), and altered strains with the RS1-CTX prophage containing the El Tor type rstR and classical ctxB on the large chromosome were placed in two MLVA groups (group II: India/Bangladesh group; group III: India/Vietnam group).

Molecular epidemiology of Vibrio cholerae O1 in northern Vietnam (2007–2009), using multilocus variable-number tandem repeat analysis

“…Although the five MLVA clones examined in this study were closely related, the clone 1 variant was maintained during 2009. This supports a previous report that VNTR loci on the large chromosome of V. cholerae are relatively stable (Choi et al, 2010) and suggests the usefulness of MLVA5 for the time frame of this study. Analysis of MLVA7 revealed relationships among isolates in greater detail, including the possibility of clone shifting through #2-08 or #2-10 strain.…”

“…As the former were presumed to change more slowly than the latter, we first analysed the isolates using the five loci of the large chromosome (MLVA5), which can be used for classifying the isolates more broadly (Choi et al, 2010). We identified five MLVA5 types (hereafter referred to as clones; Table 2).…”

“…Lastly, MLVA showed that clones 1 and 2 were related. The former emerged after and was thus likely derived from the An MLVA5 profile for VC-1, -2, -3, -5 and -6 loci of [10, 6, X, X, 7] -where X is variable -was frequently observed in Vietnam and other southeast Asian countries in (Choi et al, 2010Okada et al, 2010). Clone 2 strains with an MLVA5 profile of [10, 6, À2, 4, 7] in this study were identified in a 2010 survey of southern Vietnam and Laos (Sithivong et al, 2011;Nguyen et al, 2016).…”

“…Strains in the third wave with the cholera toxin (CTX)-3 phage have displaced the original El Tor with the CTX-1 phage in Asian countries. Since 2007, there have been several reports of cholera outbreaks or endemic cases caused by wave 3 strains in Southeast Asia (Ang et al, 2010;Okada et al, 2010;Choi et al, 2010). In Vietnam, about 20 000 cases were reported in 1964 at the beginning of the seventh pandemic of cholera; the early 1990s saw around 5000 cases per annum of cholera caused by V. cholerae O139; and in 2007, there was a large outbreak in northern Vietnam involving 1880 cases (World Health Organization, 2008) that were presumably caused by wave 3 strains (Nguyen et al, 2009;Choi et al, 2010) MLVA is a discriminatory and useful molecular epidemiological tool for studying the genetic relatedness of bacterial isolates based on the variability of VNTRs at multiple loci; the method has advantages for assessing short-term transmission of bacterial infectious diseases such as cholera (Choi et al, 2010;Moore et al, 2015).…”

Drug response and genetic properties of Vibrio cholerae associated with endemic cholera in north-eastern Thailand, 2003–2011

“…Atypical ET possessing CL biotype CTX was first reported in Asia at the start of this century (Nair et al, 2006;Raychoudhuri et al, 2008;Morita et al, 2010) and subsequently in Africa and Central America (Alam et al, 2010), including Haiti (Chin et al, 2011Hasan et al, 2012). Several genotypic variants of the Asian atypical (altered) ET were identified in Africa Choi et al, 2010) and Central America . In this study, V. cholerae O1 strains associated with cholera in Khon Kaen, Thailand, were phenotypically and genetically confirmed to be ET, but possessing CTX of the CL biotype, as reported previously in Thailand (Okada et al, 2010; Na-Ubol et al 2011).…”